Metallized polymeric finishes can be used to complement and even replace bright, reflective metal surface treatments, particularly chrome plating. Polymeric structures having metallized finishes are commonly used as substitutes for articles, such as automobile grills, that are expected to have a chrome-plated appearance. Decorative polymeric components, in fact, are becoming standard in the automobile industry, primarily because plastics are relatively flexible, corrosion-resistant, and inexpensive. Plastic parts also reduce vehicle weight, which enhances performance, especially fuel economy.
Many patents disclose metallized substrates. For example, U.S. Pat. No. 5,035,940 describes a polymer-backed aluminum substrate with a weather-resistant polymer coating. Similarly, U.S. Pat. No. 5,536,539 describes an automotive component formed from a molded polymer article having a decorative polymeric film surface. Both of these patents are commonly-assigned with the present invention.
Conventional in-situ methods of metallizing polymeric substrates often directly coat metal onto molded substrates, usually by vacuum deposition. In this regard, indium has gained acceptance as a preferred metal because on a microscopic scale it tends to form small, discrete deposits or "islands." When bent or flexed, discontinuous metal layers tend to retain the desired optical properties better than do continuous metal films, which tend to fracture. Discrete metallization also minimizes electrical conductivity, which can hasten unwanted corrosion. For example, U.S. Pat. No. 4,431,711 (Eisfeller) addresses indium metallizing three-dimensional articles in a way that minimizes electrical conductivity and, consequently, corrosion.
In most cases, the metallized layer is covered with a transparent polymeric coating that physically and chemically protects its surface--a so-called "clear coat." Although in-situ metallization of formed polymeric articles is useful, it requires separate applications of a base coat, a metallized layer, and a clear coat. This necessitates drying time for each application, which lengthens the processing times associated with metallizing three-dimensional articles. Therefore, depositing metal directly onto an article only after the article has been formed can be disadvantageous.
Alternatively, metallized film laminates (i.e., adhesive tapes) that can be applied to polymeric structures offer certain advantages over conventional in-situ metallization techniques. For example, metallized film laminates can be manufactured, stored, and shipped in roll form. Such laminates also facilitate customized application, limited only by adhesive effectiveness. Moreover, using a metallized film laminate reduces chemical compatibility problems that can arise between the metal and the polymeric substrate when metallizing articles in-situ.
To manufacture a metallized film laminate, a polymeric substrate is typically coated with a desired metal, often via vacuum deposition. Then, a polymeric clear coat is added to the metallization layer using conventional techniques, such as casting or doctor-blade applications. Using such metallized film laminates, though convenient, can result in an inferior finish as compared to that obtained by in-situ techniques. Therefore, it is desirable to achieve a finish similar to an in-situ process, yet with the convenience of a film laminate.
To that end, there are known to be metallized laminates that can be formed into desired shapes using conventional techniques. In addition, such molded laminates can be filled with thermoplastic polymer to produce a solid article having a similar bright finish as an article that has been metallized by in-situ methods.
For example, U.S. Pat. No. 4,101,698 (Dunning et al.) discloses a metallized elastomeric laminate that can provide a reflective metal surface finish for three-dimensional contoured shapes. In particular, the metallized layer is applied to an elastomeric film in separate, discontinuous planar segments. U.S. Pat. No. 4,115,619 (Kurfman et al.) discloses a bright multi-layer polymer composite formed by metallizing a thermoplastic polymer layer with a soft metal, such as indium. The metal layer is applied by conventional techniques, such as vacuum deposition, sputtering, or lamination. The metallized film can then be molded into a desired shape using conventional forming processes. U.S. Pat. No. 4,403,004 (Parker et al.) describes a metallized laminate formed of a thermoformable base layer that is coated on both sides with vapor deposited metal. This laminate is capable of being thermoformed to assume three-dimensional shapes.
Such formable film laminates have poor flexibility, however, often cracking when the metallized substrates are excessively deformed. Moreover, such moldable films tend to lose luster over time. This is particularly pernicious with respect to metallized indium layers, which in the presence of halogen-containing polymers (e.g., polyvinyl chloride, "PVC") can undergo an oxidation-reduction reaction that converts elemental indium to indium trichloride. Finally, to the extent such moldable films are formed from continuous metallized layers, corrosion problems result.
Accordingly, a need exists for a bright metallized, formable film laminate that addresses these problems.